Digital intraoral X-ray photography method and holder for picture plate or X-ray film

ABSTRACT

Intraoral dental radiography based on X-ray photography. The radiography is performed with either a conventional film or a picture plate, in which case the dimensions of the picture may be corrected by means of a computer program while viewing the picture on a monitor. Problems caused by a shallow palate because of the oblique position of the film holder may thus be eliminated, and the top of the roots of the tooth is also visible in the picture. The picture plate or film holder used in the method comprises three interlinked parts, namely a film holder, a bite portion, and an alignment rod, and one sliding part, i.e. the positioning block.

The invention relates to intraoral dental radiography based on X-rayphotography. To perform the photography method, a holder for an X-rayfilm or a digital picture plate comprising a film holder, a bite portionand an alignment rod, is used.

Traditionally dental radiography has been performed on an X-ray filmexposed by an X-ray tube. A quite simple holder comprising two positionsof which both have usually been perpendicular to the bar of the filmholder has generally been used for positioning the X-ray film inside themouth. The X-ray tube has, as a rule, been aligned by means of the bar.In many cases, X-raying with a holder has proved impossible due to thenarrowness of the mouth, the target area, and less developed filmholders. Therefore, various solutions involving cotton pads have beenapplied, whereby the patient presses the X-ray film into the desiredposition in the mouth. One such case is a shallow palate, which makes itimpossible to X-ray especially the dental root tops with existingmethods by means of a film holder. In this case the patient holds thefilm in place with his or her finger against the tooth using cottonpads, and exposure takes place almost at random, wherefore the anglebetween the film and the X-ray tube is not accurately known. Withexisting methods, the root tops do not always show on the film, andusing finger placement by means of cotton pads easily results in anobscure picture, even if the so-called bisecting angle technique wereused, as the angles are not accurately known. Introducing fingers intothe mouth and using them as film holders is naturally also unpleasantand unhygienic as far as the patient is concerned.

In conventional X-ray film holders the bar is perpendicular and theyhave two positions, one for X-raying the roots and the other forso-called bite-wing radiography intended for X-raying the crown parts ofopposing teeth. A digital picture plate is not applicable in aconventional film holder, where the slot usually is too small for thepicture plate, and its use is essentially limited by the lack ofpossibilities of changing positions. Naturally, the advantages of moderndigital technology and picture processing cannot be utilized whenconventional film holders are used or when the film is placed manually.If the angle between the digital picture plate and the X-ray tube isknown with reasonable accuracy, the digital picture may be amended on adisplay screen by a program which is designed for this purpose, andwhich will take into account the set angles and the distance between thepicture plate and the X-ray tube, and will automatically calculate thecorrections for the distortions they have caused. Conventional X-rayingmethods are slow, and the results may not be read until the picture hasbeen developed. A digital picture is immediately readable.

Up to now, one of the problems has also been the difficulty ofre-exposing in view of the so-called subtraction technique, as X-rayingin exactly the same place and the same position has been problematic. Ithas also been difficult to X-ray files used in root canal therapy whilethey are positioned in the canals.

By the method and the holder for a picture plate or X-ray film of theinvention, a decisive improvement may be attained over the existingmethods.

The digital intraoral X-ray photography method of the invention and theholder for a picture plate or X-ray film applied therein arecharacterized by that which is set forth in the attached claims.

By means of the new method and device of the invention, intraoralX-raying becomes more hygienic, more reliable, easier and faster. Theholder of the invention may be used in nearly all intraoral radiographs,including cases where the so-called cotton pad technique is currentlyapplied. The holder may be used in all intraoral radiographs of theareas of the maxilla and mandible, and in the so-called bite-wingradiography, where the crown parts of upper and lower jaw teeth of thesame side are X-rayed simultaneously. When the picture plate photographyof the invention is used, applying the so-called bisecting angletechnique becomes easier, and by the use of the desired film angle andan accordingly aligned alignment rod, more accurate results areobtained. The measuring scales may be synchronized so that the angle ofthe X-ray tube, as shown by the indicator rod, complies with thestandard values of the bisecting angle technique, whereby the bestphotographing result is obtained even with conventional dental filmtechniques. This is especially important in e.g. assessing the length ofthe root canal in root canal therapy, when the right dimensions arecrucial to the success of the therapy. By means of a holder theprobability of getting accurate pictures will increase, and the need forre-exposure and the amount of radiation to which a patient is exposedare decreased. This is a more hygienic and pleasant manner of takingradiographs as compared to the cotton pad technique, as the patient hasno need to introduce a finger into the mouth. The device of theinvention is anatomically designed. The intraoral parts are detachable,allowing easier and more effective sterilization. The film slotaccommodates both a dental film and a digital picture plate, which doesnot usually fit in the prior art devices. Applied to a digitalradiographic method, the method of the invention will open new prospectsfor intraoral radiography. The X-ray tube may be aimed orthogonally tothe object, and to a certain limit the film angle may be oblique inrelation to the object and still the X-ray pictures will have the rightdimensions. This is achieved by a computer utility program which willcalculate, on the basis of the given film angle and, if needed, also theangle and distance of the X-ray tube, the right dimensions for theobject being X-rayed. The method of the invention also allows precisere-positioning when follow-up exposures are taken. This is achieved bymeans of bite blocks on top of which impression agent is administered;when solidifying, the agent will retain its form and adhere to the biteblock.

In the following the invention will be described in greater detail withreference to the accompanying drawings:

FIG. 1 is a top view of a holder for a picture plate or an X-ray film.

FIG. 2 is a side view of a holder for a picture plate and an X-ray film.

FIG. 3 shows the positioning block of an X-ray tube.

FIG. 4 is an enlarged side view of an X-ray film holder.

FIG. 5 shows the fastening mechanism of a film holder and a biteportion.

FIG. 6 shows a protective cover to be attached to a bite portion for usein root canal therapy.

FIG. 7 shows a bite portion used in positioning.

FIG. 8 shows positioning of an X-ray tube and a film holder in a case ofnew digital X-raying.

FIG. 9 shows positioning of an X-ray tube and a film holder inradiography using the bisecting angle technique.

In FIGS. 1 to 5, numeral 1 refers to a film holder and numeral 2 to abite portion, to which an alignment rod 3 is joined. Numeral 4 denotes afilm or a picture plate. Joints are denoted by numerals 5 and 6. Thebite portion 2 is provided with detachable additional pieces 7. The biteportion 2 comprises a hole 8, whereon additional pieces of the biteportion are attached, and said hole may be used when accommodating rootcanal files. The angles formed by the joints 5 and 6 are readable onscales 9 and 10. The holder for a picture plate or film 1 is attached tothe bite portion by means of an axle 11 comprising grooves 12. The axle11 is placed into slots 13 and 14, comprising respective grooves 12 onthe inside, and to allow installation, one of the slots, i.e. slot 14,has been split. Numeral 16 denotes a back plate and numeral 17 a frontplate of the film holder 1. Numeral 18 denotes a slot therebetween. Forbite-wing radiography, the back plate 16 of the film holder 1 isprovided with a tubular and partly open clamp 19 to facilitate fasteningof the axle 11. Numeral 20 refers to a positioning block for the X-raytube; the positioning block comprises three branches 21, 22, 23, and itslides on the slot 14 along the alignment rod 3.

In FIG. 6, numeral 26 refers to a tooth and numeral 27 to its root.Numeral 28 denotes a root canal file and numeral 29 a cover. In FIG. 7,the bite portion 2 comprises bite blocks 30, which are treated withimpression agent that will harden for the purpose of re-positioning.

FIGS. 8 and 9 schematically show the photography method. Numeral 31refers to an X-ray tube and numeral 32 to the palate.

When a film holder of the invention is used in conventional dentalradiography, the film holder 1 is positioned inside the mouth, and thepatient will bite on the additional pieces 7 in the bite portion 2, thussecuring the desired position of the holder. Before exposure, thedesired angle of the film holder 1 has been set by means of a joint 5,and the width of the angle is readable on a display scale 9. A joint 6,between the bite portion 2 and an alignment rod 3, is provided with ascale 10, by means of which the right angle may be set for the X-raytube in accordance with the bisecting angle technique. By the use ofdigital technology and picture processing methods corrected by microprocessors, a digital picture plate may, in accordance with the size ofthe mouth, be placed in a suitable angle to allow the top of the root 27of a tooth 26 also to show, and the X-ray tube 31 may be positionedperpendicularly to the tooth. With the digital picture plate 4 in anoblique position and the X-ray tube 31 in a straight position, thepicture will naturally stretch, but by means of a picture processingprogram this may be corrected, and thus the resulting picture is similarto the one obtained when X-raying perpendicularly to the film. Theconventional bisecting-angle technique may also be used in processingthe digital picture if the top edge of the root does not show in thepicture when direct radiography is used.

By means of a three-branched positioning block 20, fastened around thealignment rod 3, the X-ray tube 31 may be positioned correctly dependingon whether ordinary or bite-wing radiography is used. Additionally, thedistance and position of the X-ray tube may be defined by thepositioning block 20. The reading is given on a scale 25, and beamdispersion may be taken into account.

The holder of the invention comprises four different parts andadditional equipment, of which the film holder 1, is detachable. Thefilm holder 1, the bite portion 2, and the alignment rod 3 areinterlinked by joints 5 and 6 comprising scales 9 and 10 for reading ofangles, and the X-ray tube positioning block 20 is slidably connected tothe alignment rod 3. The joints 5 and 6, and their parts, are indentedto allow desired positioning by means of certain angle adjustments. Forbite-wing radiography, the back plate 16 of the film holder comprises aclamp 19 allowing perpendicular attachment of the back plate 16 from itsmiddle part to the bite portion 2. The bite portion 2 and its hole 8 areequipped with additional pieces 7 of different thicknesses according tothe need. The additional pieces 7 are usually made from bite-resistant,semihard material. The film holder 1 and the bite portion 2 are placedinside the mouth of the patient, and are thus anatomically designed inan optimal way. The film holder 1 with the attached bite portion 2 andthe alignment rod 3 are made from non-toxic, roentgen-negative plasticstolerating steam-sterilization, and are thus reusable aftersterilization. In case repeated so-called subtraction pictures must betaken of the patients mouth for follow-up, bite blocks 30, disposedwithin the holes 8 of the bite portion 2, are provided with biteimpressions hardened by means of an impression agent, to allow the filmholder or picture plate to be placed in its original position by meansof the bite impressions. Naturally, the joints 5 and 6 have to bepositioned according to the original values of the positions.

In root canal therapy, when root canal files 28 have been used, theproblem has been to determine their depth. When a cover 29 mountable onthe bite block 2 is used, pictures may be taken relatively easily bymeans of the film holder and the X-ray tube, and the penetration of thefiles may be accurately determined.

Naturally, the digital intraoral X-ray photography method of theinvention will lead to new applications and facilitate and expand thepossibilities of intraoral radiography. The holder for a picture plateor film applied in the method of the invention may naturally assumeother forms than those disclosed in this application. Also the structureof the joints attached to the film holder may be different, and theangular scales 8 may be located otherwise than in the embodiment of thisapplication without departing from the scope of the inventive concept.

I claim:
 1. In a method for digital or film-based intraoral dental x-rayphotography, wherein a holder for a picture plate or film is held inplace in the mouth of a patient, and the picture plate or film is placedat a desired angle in relation to a tooth being x-rayed with radiationemitted from an x-ray tube, the improvement comprising the steps of:(a)collecting data as to (i) an angle between the picture plate or film andthe tooth, (ii) an angle between the x-ray tube and the tooth and (iii)a distance between the x-ray tube and the tooth; and (b) correcting animage distortion resulting from a non-orthogonal disposition betweensaid tube and said tooth or between said tube and said picture plate orfilm based upon the data collected in step (a).
 2. A method as claimedin claim 1, comprising displaying an image of the tooth on a displayscreen of a computer and correcting the image by providing the computerwith the data collected in step (a) and with a program that causes thecomputer to process the data to display the image on the display screenwithout the image distortion.
 3. A method as claimed in claim 1 whereinthe holder comprises a bite block and an alignment rod, wherein the datacollected in step (a) as to the angle between the picture plate or filmand the moth is generated by measuring an angle between the pictureplate or film and the bite block, wherein the data collected in step (a)as to the angle between the x-ray tube and the tooth is generated bymeasuring an angle between the bite block and the alignment rod andwherein the data collected in step (a) as to the distance between thex-ray tube and the tooth is generated by measuring a distance betweenthe x-ray tube and the bite block.
 4. A method as claimed in claim 2wherein the holder comprises a bite block and an alignment rod, whereinthe data collected in step (a) as to the angle between the picture plateor film and the tooth is generated by measuring an angle between thepicture plate or film and the bite block, wherein the data collected instep (a) as to the angle between the x-ray tube and the tooth isgenerated by measuring an angle between the bite block and the alignmentrod and wherein the data collected in step (a) as to the distancebetween the x-ray tube and the tooth is generated by measuring adistance between the x-ray tube and the bite block.
 5. An apparatus fora picture plate or film used in intraoral x-ray photography of a tooth,comprising a film holder, a bite portion, an alignment rod for aligningan x-ray tube, first joint means for joining the film holder and thebite portion so that they can be adjustably disposed with respect to oneanother at any of a plurality of angles, second joint means for joiningthe bite portion and the alignment rod so that they can be adjustablydisposed with respect to one another at any of a plurality of angles,scale means for collecting data concerning an angle between the filmholder and the bite portion, concerning an angle between the biteportion and the alignment rod, and concerning a distance between thex-ray tube and the tooth, and processing means for processing the datacollected by the scale means and for using the processed data to correctfor imaging distortions in the x-ray photography.
 6. An apparatus asclaimed in claim 5, wherein the scale means comprises a plurality ofscales and wherein the first and second joint means comprise respectivefirst and second joints, each of said first and second joints comprisingan axle and a slot that are grooved, each said joint being provided withone of the plurality of scales.
 7. An apparatus as claimed in claim 5,comprising a positioning block for the x-ray tube connected to thealignment rod so as to slide back and forth along it, said positioningblock comprising a plurality of branches adapted to function asadjusting points, the alignment rod comprising a scale for providing theprocessing means with data concerning the distance between the x-raytube and the tooth.
 8. An apparatus as claimed in claim 5, comprising aplurality of additional pieces attached to the bite portion by a hole inthe bite portion, said additional pieces providing a spacing betweenupper and lower teeth of a patient to be treated.
 9. An apparatus asclaimed in claim 8, wherein the additional pieces comprise biteimpressions cured onto the surfaces of the additional pieces with animpression agent, whereby said bite impressions provide an indication asto an original position of the upper and lower teeth in follow-upprocedures.
 10. An apparatus as claimed in claim 8 comprising a coverattached to a top of the bite position and a root canal file in the holeof the bite portion.
 11. An apparatus as claimed in claim 6, wherein theslot of each of said joints has a part that is partially opened to allowfor insertion of a respective one of the axles, each slot and axle beinggrooved to allow for graded adjustment therebetween.